Background: Twenty percent of HIV-positive Latinos are not aware of their HIV status, and over half are diagnosed late. Persons with undiagnosed HIV infection can continue risky sexual and drug-related behavior and unknowingly put others at risk. Additionally, delayed HIV diagnosis has been shown to increase the risk of poor health outcomes and HIV-related mortality. Predictors of delayed HIV diagnosis among Latinos include older age, male gender, injection drug use (IDU), foreign birthplace, and low educational attainment. Studies suggest that neighborhood characteristics may also predict healthcare utilization and health outcomes and partially account for racial/ethnic disparities. Moreover, studies show that neighborhood factors, independent of individual factors, also predict HIV seroconversion and high-risk injection behavior among IDUs. Objective: The objectives of this study are to (a) examine the relationship between neighborhood characteristics and delayed HIV diagnosis among Latinos of varying origins, and (b) identify the potential moderating effects of IDU on these associations. Specifically, the study will examine the impact of neighborhood-level socioeconomic status (unemployment, poverty, and educational attainment) and ethnic density on the timing of HIV diagnosis among Latinos by country or region of birth. Design: The study will use a cross sectional study design to study Latino individuals [13 years and older] reported with HIV infection between 2007 and 2011 to the Florida Department of Health HIV/AIDS Reporting System. The American Community Survey conducted by the U.S. Census Bureau will be used to determine neighborhood characteristics. Cases will be matched to neighborhood characteristics based on the zip code of residence at the time of HIV diagnosis. The total sample size is [5,899]. Analysis: Mixed/random effects modeling will be used to determine the effect of neighborhood- level factors on delayed HIV diagnosis. This method will account for non-independence (spatial correlation) within and between neighborhoods. An interaction term between neighborhood-factors and injection drug use will be added to the model to test for IDU as a moderator of the relationship between neighborhood-factors and delayed HIV diagnosis. Analysis will be stratified by country/region of birth to account for the large socioeconomic, educational attainment, and health care access variability among Latinos of varying origins as well as the differences in history of IDU. Significance: [The results of this study will help identify possible structural barriers to and facilitators of HIV testing among Latinos of varying origins. This information will assist public health professionals to appropriatey target resources and design more effective and culturally competent interventions to decrease the risk of delayed HIV diagnosis among Latinos.] The aims of this study are parallel to NIH/NIDA's strategic plan to decrease health disparities of HIV/AIDS, prevent HIV transmission, and better understand the interaction of drug abuse and HIV/AIDS.